This disclosure relates to the field of utility meters, and particularly to processes for tracking components in meters and recalling potentially defective meters for repair.
Electric companies install electricity meters at various locations in order to monitor the amount of electricity consumed by customers. Unfortunately, electricity meters are subject to occasional failure. When an electricity meter fails, it will likely incorrectly record the amount of electricity used by the customer, and the customer may be over-billed or under-billed for electricity consumption.
Failures in electricity meters often result from defective electronic components. In particular, electricity meters include a printed wiring board (PWB) that supports most of the electronic components for the meter. Manufacturers of the electricity meters often outsource pre-assembled PWBs from a supplier. In such a case, once the PWBs arrive from the supplier, the manufacturer of the electricity meter installs the pre-assembled PWB in the meter housing along with the other components of the meter.
Electricity meter failures due to defective electronic components often stem from a defective manufacturing process, or a defective group of parts used during the manufacturing process, including defective parts placed on the PWB during manufacture of the PWB. As a consequence, when an individual meter fails, there is a greater likelihood that other meters manufactured at or about the same time will also fail. Furthermore, if the problem with the meter can be traced to a particular component within the meter, there is a greater likelihood that other meters containing the same components from the same lot will have the same problem. For example, if a meter fails due to a defective resistor, there is a higher probability that other meters will fail that are manufactured from the same lot of resistors.
Accordingly, in order to reduce potential failures, manufacturers may preemptively repair meters that are likely to have the same problem as an already defective meter. To this end, serial numbers on the meters can be used to identify meters made at about the same time. In particular, these serial numbers identify the date the meter was assembled. With this information in hand, if a defective meter is identified, other meters with the same manufacturing date can be tracked and tested for the same problem. Unfortunately, serial number tracking to identify meters that were assembled at the same time often results in inaccurate identification of affected meters. In particular, meter serial numbers do not necessarily track to lots of individual components, particularly when PWBs are populated by an outside supplier.
When a meter manufacturer identifies a particular lot code/number for a defective component, the current method for identifying other meters that might have the same potentially defective part starts with identifying the serial number on the meter. Using the meter serial number, the manufacturer can identify other meters that were made near the same date and time as those meters may contain a component having the identified component lot code. However, not all meters made within a particular time period will necessarily contain the potentially defective component. For example, pulling all meters made on the same day as the defective meter will often result in the return of a large number of components that do not contain components from the defective lot, as it is not uncommon for a first lot of components to be used when assembling meters early in a day, while a second lot of components is used later in the day, after the first lot of components is gone.
While there is no guarantee that meters made on the same day and near the same time comprise components from the same component lots, it is also true that meters made on different days may contain components from the same component lot. This is especially the case when components used in the meters are subjected to sub-processing before they are placed on the PWBs for the meters. For example, assume the leads of a resistor must be cut to a certain length by the PWB manufacturer before the resistor is placed on the PWB. After receiving a lot of resistors from the resistor supplier, the PWB manufacturer cuts the resistor leads and transfers the resistors to an assembly bin where the resistors are mixed with resistors from other lots. During assembly of any group of PWBs, the resistors are randomly selected from the assembly bin and populated on the PWBs. Thus, a number of resistors from a given lot may be used on a given day, while several other resistors from this same lot may remain in the bin for some time until they are randomly removed during a different assembly process.
As described in the preceding paragraphs, meters made on the same day and near the same time do not always comprise components from the same component lots. Likewise, meters made on different days over significant periods of time may contain components from the same component lot. Therefore, once a defective lot of components is identified, meter manufacturers are forced to take a conservative approach and check all meters manufactured within extended time frames in order to determine if such meters contain components from the identified lot. This process of identifying other potentially affected meters is known as “bracketing”, as large groups of meters made over contiguous time periods are grouped or “bracketed” together in an attempt to inspect the meters most likely containing components from the identified lot. Of course, this inaccurate method of identifying potentially affected meters forces the manufacturer to inspect more meters than those that actually contain components from the identified lot. Furthermore, if the chosen review bracket is too small, some meters will be missed. Nevertheless, even if no affected meters are missed, unaffected meters are almost always inspected and have to be returned to the field. The sorting and other labor involved with the bracketing process results in significant additional costs to the manufacturer.
Accordingly, it would be advantageous to provide a method for tracking components in an electricity meter wherein a serial number is used to not only track the manufacturing date and lot number, but the serial number is also used to identify discrete components within the meter and the component lots.